1. Field of the Invention
The present invention relates to a pinch roller apparatus used for a tape driving apparatus in a video tape recorder, an audio tape recorder and the like.
2. Description of the Prior Art
The pinch roller apparatus used for the tape driving apparatus is structured such as to grip a tape between a pinch roller main body and a capstan and feed the tape in accordance with a driving operation of the capstan. In order to securely feed the tape moving between the pinch roller apparatus and the capstan in a stable state, the pinch roller apparatus is required a self-aligning function for following an incline of the capstan. Accordingly, a bearing having a self-aligning function is employed for the pinch roller apparatus.
In recent years, in place of an expensive ball bearing, for example, a resin plain bearing described in Japanese Patent Unexamined Publication No. 10-49935 and 10-228692 or an oilless plain bearing described in Japanese Utility Model Publication No. 8-9447 are used for the bearing of the pinch roller apparatus having the self-aligning function.
The pinch roller apparatus mentioned above is generally structured in the following manner. That is, the pinch roller apparatus is formed by providing a rubber-like elastic body on an outer periphery of a sleeve made of a metal such as an aluminum, a brass and the like or a resin so as to form a pinch roller main body and pressure fitting the plain bearing into the sleeve. Then, it is mounted by inserting a pinch roller shaft having one end mounted to an arm into the plain bearing. The pinch roller apparatus is structured such as to press the pinch roller main body to the capstan by moving the arm so as to grip the tape. The self-aligning function of the pinch roller corresponds to an operation of making a rotary shaft of the pinch roller main body in parallel to the capstan due to a clearance between the pinch roller shaft and the plain bearing.
As mentioned above, the self-aligning function in the conventional pinch roller apparatus is performed by the pinch roller main body being inclined in a direction of the capstan due to the clearance between the pinch roller shaft and the plain bearing. However, the pinch roller main body is also inclined in a direction perpendicular to the direction of the capstan in addition to the direction of the capstan, that is, a moving direction of the tape. Accordingly, in view of a moving stability of the tape, it is preferable that the clearance of the plain bearing corresponding to the incline of the pinch roller main body is set as small as possible.
Further, in the case that the plain bearing is a resin plain bearing, it has been hard to secure an accuracy of a size since a shrinkage is generated after being formed by a metal mold. Further, the plain bearing is, as mentioned above, assembled by being pressure fitted into the sleeve forming the pinch roller main body. However, an inner diameter of the sleeve itself is not always fixed and the plain bearing is shrunk in a radial direction at a time of being pressure fitted into the sleeve. Accordingly, it has been significantly hard to accurately form the inner diameter of the plain bearing at a time of assembling as the pinch roller due to an error of the inner diameter of the sleeve as well as an error in a size of the plain bearing itself.
Further, when the clearance between the pinch roller shaft and the plain bearing is too small, a smooth rotation of the pinch roller main body is restricted, and it is impossible to obtain a sufficient self-aligning function. On the contrary, when the clearance between the pinch roller shaft and the plain bearing is too large, as well as a durability of the plain bearing is deteriorated, there is a problem that it is impossible to stably move the tape due to a point contact between the capstan and the roller main body.
On the contrary, the pinch roller apparatus described in Japanese Patent Unexamined Publication No. 10-228692 is structured such as not to self-align in accordance with the clearance but to self-align in accordance with an elasticity of the plain bearing, in order to solve the problem generated in the case that the clearance between the pinch roller shaft and the plain bearing is large. Accordingly, as well as the plain bearing is made of a resin, Young""s modulus of the resin is set to 10 kgf/mm2 or more and 200 kgf/mm2 or less. Further, in the case that one or a plurality of gap portions for facilitating a shape change are provided in the resin plain bearing, the Young""s modulus of the resin may be set to 50 kgf/mm2 or more and 1500 kgf/mm2 or less.
Then, the pinch roller apparatus disclosed in the publication mentioned above is structured such that the rotary shaft of the roller main body and the rotary shaft of the capstan are made in parallel to each other due to an elasticity of the resin constituting the plain bearing and the inner peripheral surface of the plain bearing can slide in a state of being nearly in a surface contact with the inclined roller shaft. It is said that accordingly, since the roller shaft and the inner peripheral surface of the plain bearing are not in a point contact state even in a state that the self-aligning function is served, a part of the plain bearing is not abnormally abraded, so that it is possible to sufficiently secure a durability of the pinch roller even in the case of the resin plain bearing.
However, since the pinch roller apparatus described in Japanese Patent Unexamined Publication No. 10-228692 mentioned above is self-aligned in accordance with an elasticity of the resin constituting the plain bearing, there is a risk that the plain bearing generates a fatigue fracture after being used for a long time. Further, since the pinch roller apparatus mentioned above self-aligns in accordance with an elasticity of the resin not with the clearance, much time is required before the pinch roller main body becomes in parallel to the capstan, so that there is a problem that it is impossible to self-align for a short time.
Further, in the pinch roller apparatus described in Japanese Patent Unexamined Publication No. 10-228692 mentioned above, since the elastic operation is different between the gap portion and the non-gap portion in the case of providing a plurality of gap portions in the plain bearing, a bending amount of the plain bearing is different between a time when the inner peripheral surface of the gap portion of the plain bearing is brought into contact with the roller shaft and a time when the inner peripheral surface of the non-gap portion of the plain bearing is brought into contact with the roller shaft, so that there is a risk that a moving operation of the tape becomes uneven. Further, the pinch roller apparatus mentioned above is structured such as to set a contact area between the roller shaft and the plain bearing when pressing the roller main body to the capstan to be great. Accordingly, since an amount of a power consumption of a capstan motor becomes significantly increased, it is not preferably applied to the pinch roller apparatus for a camera integral-type compact video tape recorder and a compact audio tape recorder which are driven by a battery..
The present invention is made by taking the current circumstances into consideration, and an object of the present invention is to provide a pinch roller apparatus having the following objects.
One of the objects of the present invention is to provide a pinch roller apparatus which can stably move a tape in accordance with a sufficient self-aligning function.
Another object of the present invention is to provide an inexpensive pinch roller apparatus as a structure which can easily manufacture a plain bearing.
Further, the other object of the present invention is to provide a pinch roller apparatus in which an assembly of the pinch roller can be easily performed at a time of inserting a pinch roller shaft into a plain bearing pressure fitted to a sleeve so as to assemble the pinch roller.
Still further, the other object of the present invention is to provide a pinch roller apparatus which can secure a good tape movement by making a clearance small so as to reduce an incline in a moving direction of the tape.
Furthermore, the other object of the present invention is to provide a pinch roller apparatus which can reduce an amount of a power consumption of a capstan motor.
Moreover, the other object of the present invention is to provide a pinch roller apparatus in which a self-aligning function can be securely performed for a short time.
The present invention is structured as follows for achieving the objects mentioned above. That is, a pinch roller apparatus in accordance with the present invention is structured such as to mount a pinch roller main body provided with a rubber-like elastic body on an outer periphery of a sleeve via a plain bearing to a pinch roller shaft having one end fixed to an arm and press the pinch roller main body to a capstan by moving the arm. A circular sliding plate brought into contact with both of an upper end surface and a lower end surface of the plain bearing is mounted to the pinch roller shaft, and an end cap is adhered to a front end portion of the pinch roller shaft. When setting a length of an axial gap between the circular sliding plate brought into contact with the upper end surface of the plain bearing and the plain bearing to A and a length of an outer diameter of the circular sliding plate to B, the structure is made such as to satisfy a relation 0.007xe2x89xa6A/Bxe2x89xa60.06. By setting the relation between A and B so that the plain bearing is inclined at the range mentioned above, it is possible to reduce a width for self-alignment. Accordingly, it is possible to restrict the incline in the moving direction of the tape to a small level and it is possible to secure an improved movement of the tape.
Further, when setting a clearance in a diametrical direction between the pinch roller shaft and the sliding surface of the plain bearing to X and an effective length of the sliding surface of the plain bearing to Y, it is preferable to structure so as to satisfy the relation X/Yxe2x89xa70.052. By making the structure so that X and Y satisfy the relation mentioned above, the clearance between the pinch roller shaft and the sliding surface of the plain bearing has a sufficient magnitude. Accordingly, the plain bearing and the sleeve to which the plain bearing is pressure fitted may be structured so as to be over a designed error of size, so that it is easy to form the plain bearing and assemble the pinch roller apparatus. In accordance with the present invention, as is different from the conventional method of aligning in response to the clearance X in the diametrical direction between the pinch roller shaft and the plain bearing, for preference, the clearance X is formed greater than the conventional one and an amount of alignment is adjusted in accordance with a length of a gap in an axial direction at upper and lower ends of the plain bearing.
In one aspect of the present invention, both end surfaces of the plain bearing mentioned above are formed in a taper-like or circular arc-shaped inclined surface in a radial direction toward an outer peripheral surface from a center portion of the shaft. The circular sliding plate brought into contact with both of the upper end surface and the lower end surface of the plain bearing is inserted into the pinch roller shaft having one end fixed to the arm. In the case of forming both end surfaces of the plain bearing in the taper-like or circular arc-shaped inclined surface in the radial direction toward the outer peripheral surface from the center portion of the shaft, since both end surfaces of the plain bearing can be inclined in a state of sliding on the circular sliding plate, it is possible to restrict the length of the gap in an axial direction as small as possible, so that it is possible to move the tape in a stable state.
In one aspect, the plain bearing forms a sliding surface which is parallel to an axial direction of the plain bearing at a center portion of the inner peripheral surface, and forms a taper-like or circular arc-shaped non-sliding surface which is gradually expanded in a radial direction toward the end portion of the plain bearing from both end portions of the sliding surface. A length of the parallel sliding surface is not particularly limited, however, it is preferable to be set to 10 to 30% the length of the plain bearing. Further, the inner peripheral surface of the plain bearing may be formed in a parallel sliding surface substantially at a whole portion except a beveling portion in both end portions.
Further, in the embodiment mentioned above, the plain bearing is formed in a solid cylindrical shape, however, in another embodiment, it may be structured such that the plain bearing is constituted by an inner cylinder and an outer cylinder and a hollow gap open to at least one end surface is provided between the inner cylinder and the outer cylinder. The hollow gap extends in an axial direction. The structure may be made such that the hollow gap is open to only one end surface of the plain bearing and another end surface is closed, or may be made such that the hollow gap is open to both end surfaces and the inner cylinder and the outer cylinder are connected at a center portion. Further, it is a matter of course that the aspects mentioned above can be independently structured, and the aspects may be combined. For example, it is possible to combine the shape of both end surfaces of the plain bearing and the shape of the inner peripheral surface. Further, it is possible to combine the structure of the hollow gap of the plain bearing and the shape of the inner peripheral surface. Still further, it is possible to combine the shape of both end surfaces of the plain bearing and the structure of the hollow gap. Otherwise, it is possible to combine all the structures to form the plain bearing.
The plain bearing mentioned above is made of a self-lubricating resin. As the self-lubricating resin, it is possible to employ, for example, one or two or more of a fluorine resin, a polyester resin, a polyether sulfone resin, a polyolefine resin, a polyacetal resin, a polyamide resin and a polyphenylene sulfide resin.
Further, the pinch roller apparatus in accordance with the invention can be structured such that the plain bearing is made of a self-lubricating resin having a Young""s modulus 1600 kgf/mm2 or more. By employing the resin having the Young""s modulus 1600 kgf/mm2 or more, an abrasion of the plain bearing is significantly small even when the plain bearing and the roller shaft slide in a state of being in a point contact. Further, since the contact area between the plain bearing and the roller shaft is small, it is possible to restrict an amount of a power consumption of the capstan motor to a low level, so that it is preferably applied to a camera integral-type compact video tape recorder and a compact audio tape recorder which are driven by a battery.
Further, a self-aligning function of the plain bearing made of the self-lubricating resin having the Young""s modulus 1600 kgf/mm2 or more is not achieved by an elasticity of the resin but achieved by the clearance with respect to the roller shaft. Accordingly, the pinch roller main body can immediately follow the incline of the capstan, a time before the pinch roller main body becomes in parallel to the capstan, that is, a self-aligning time requires a short time, so that it is possible to move the tape in a good condition. Further, by employing the resin having the Young""s modulus 1600 kgf/mm2 or more, the inclined surface of the plain bearing is not deformed even when being brought into contact with the circular sliding plate as well as there is no risk of generating a fatigue fracture even after being used for a long time, so that the incline of the plain bearing can be securely restricted, and the self-aligning function can be smoothly achieved.
In the plain bearing employing the resin having the high Young""s modulus, it is also possible to form the inner peripheral surface in a linear parallel surface from one end surface to another end surface, however, a shape of the plain bearing is not particularly limited. Accordingly, in the plain bearing employing the resin having the Young""s modulus 1600 kgf/mm2 or more, the structure may be made such that a linear parallel surface is provided at a center portion so as to form a taper-like or circular arc-shaped expanded surface which gradually expands in a radial direction from both end portions of the parallel surface toward the end surface of the plain bearing. Further, in the case of forming both end surfaces of the plain bearing in the taper-like or circular arc-shaped inclined surface in the radial direction from the center portion of the shaft toward the outer peripheral surface, and in the case of being constituted by the inner cylinder and the outer cylinder and being provided with the hollow gap open to at least one end surface between the inner cylinder and the outer cylinder, it is preferable to insert the circular sliding plate which is brought into contact with both of the upper end surface and the lower end surface of the plain bearing.
Further, also in the case that a plurality of hollow gaps are provided in the plain bearing, since the elastic operation is not different between the hollow gap portion and the non-gap portion due to the construction of the resin having the high Young""s modulus, a substantially fixed being amount can be obtained and it is possible to secure a uniform tape movement.
As the resin having the Young""s modulus 1600 kgf/mm2 or more, it is possible to employ a polyamide resin, a polyphenylene sulfide resin, a polyether nitrile resin, a polyimide resin and the like.